Regional Geology of Pierce Member of Upper Morrow Formation in Anadarko Basin, with a Detailed Look at South Dempsey Field in Roger Mills County, Oklahoma: ABSTRACT

Abstract

The members of the upper Morrow formation in the deep Anadarko basin are extremely prolific but elusive targets. The high reserve potential attributable to these reservoirs has been responsible for the ranking of Roger Mills County, Oklahoma, as the leading gas-producing county in the state. The deposition of the Pierce, one of the oldest members of the upper Morrow, was a result of upward movement, during the late Morrowan, of Mississippian Meramec-Osage age sediments along the Amarillo-Wichita uplift, that were unroofed by erosion and deposited as coastal alluvial fans. High-energy traction currents, associated with fluvial channels, carried sediments 10-17 mi northeast, away from the mountain front, and deposited them in sinuous to braided patterns. Textural interpretations from core data of the Pierce show an immature, very poorly sorted conglomerate consisting of medium to coarse-grained quartz sand with pebble to cobble-sized angular and subrounded chert clasts. The Pierce has productive thicknesses ranging from 8 to 60 ft with porosities of 9 to 15% and estimated per-well reserves from 8 to 30 bcf of gas. Although the irregular depositional patterns associated with the Pierce present a challenge to the explorationist, the accompanying prolific production, characteristic of this reservoir, has made it onemore » of the more rewarding targets in Oklahoma. Further understanding of the petrology and depositional environment of the Pierce will aid in the delineation of future exploration plays within both this unit and other members of the upper Morrow formation deposited under similar conditions.« less